showing 36 of ~574560 from 574555 documents
Benzodiselenagermoles and spirobisbenzodiselenagermoles
1993
Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by 1H, 77Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.
Spectral investigation of spin echo emission
1993
Abstract The spectral content of the echo radiation emitted after a two-pulse sequence is measured in a two-level spin system. The spectral profiles exhibit maxima and zeroes of spectral density depending on the exciting sequence parameters. A calculation based on a vectorial model relates the zeroes to those packets that happen to be transparent to the second (refocusing) pulse. Moreover we report on a new spectral narrowing effect which we tentatively ascribe to the instantaneous diffusion.
Search for a non-minimal Higgs boson produced in the reaction →
1993
Abstract A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e + e − → hZ ∗ . The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e− pair which could originate from the standard model background process e + e − → e + e − v v . Upper limits for the cross-section of the reaction e + e − → hZ ∗ have been derived as a function of mh, the mass of the Higgs…
Pressure dependent arrangement of a protein in two-dimensional crystals specifically bound to a monolayer
1993
Abstract The arrangement of streptavidin bound to a biotinylated monolayer of a polymeric amphiphile at the air-water interface is studied as a function of lateral pressure or ligand density. Closely packed domains are observed by fluorescence microscopy. The arrangement of the protein in these domains is sensitively detected by X-ray reflectivity and an especially thorough data analysis yields the following: the distance of the protein from the air-monolayer interface varies with lateral pressure by 10 A; the interfaces involving the protein are much rougher than expected due to capillary waves; the electron density of the protein layer increases considerably on compression, which can be u…
A study of λ+c decays into pK−π+, pK−π+π0and pK−π+π0π0
1993
Abstract In the CERN NA32 experiment a high-resolution silicon vertex detector and a purely topological approach were used to collect a clean sample of λ + c decays into pK − π + with or without additional neutral particles. We study the subresonant structure of the λ c + peak obtaining BR (λ c + → p K ∗0 (892)) = 0.35 −0.07 +0.06 ±0.03 with respect to the total λ c + → pK − π + decay. We also determine branching ratios for some channels with neutral decay products, namely BR( λ c + → pK − π + π 0 ) = 0.73±0.12±0.05 and BR( λ c + → pK − π + π 0 π 0 = 0.16±0.07±0.03, again with respect to the total λ c + → pK − π + decay.
Flow injection flame atomic spectrometric determination of iron, calcium, magnesium, sodium and potassium in ceramic materials by using a variable-vo…
1993
A series of different ceramic materials, such as porcelain, feldspar, kaolin, varnish, clay and stoneware have been analyzed. Iron, calcium and magnesium have been determined in these materials by flame atomic absorption and sodium and potassium by flame emission. The use of a variable-volume injector enables one to carry out these analyses in a flow system (after fusion of samples with lithium metaborate) and does not require different dilutions for the determination of each type of sample considered, nor the use of different flow injection manifolds. The developed procedure provides a limit of detection of 100 μg/l for Na, 70 μg/l for Ca, 50 μg/l for both Fe and K and 8 μg/l for Mg. The c…
Short-lived luminescence of mixed silver halides
1993
Abstract Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr1−xClx, (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag0i and Ag2+V-c. It is shown that the effective activation energy of Ag0i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its a…
Synthesis of two natural 8-oxo-β-cyperone derivatives from (−)-santonin.
1993
Abstract This paper reports on the chemical transformations of (−)-santonin into (+)-8-oxo-β-cyperone and (+)-12-hydroxy-8-oxo-β-cyperone involving 8-oxo group introduction and elaboration of the side chain.
Adjuvant Intravesical Chemotherapy in Patients with Primary T1 G3 Transitional Cell Carcinoma of the Bladder
1993
The Authors present their experience with TUR plus adjuvant intravesical chemotherapy in 50 patients affected by primary T1 G3 bladder tumours without previous or concomitant carcinoma in situ. At a mean follow-up of 36 months, 84% of the patients are alive and tumour-free. Cystectomy was performed in three patients due to locally invasive disease. Five patients (10%) died of bladder cancer.
Dynamic anomalies at the glass transition of organic van der Waals liquids
1993
Abstract The paper discusses the question of whether there is a characteristic temperature T c above the calorimetric glass transition temperature T g . Mode-coupling theory (MCT) predicts a crossover from liquid- to solid-like dynamics at T c . Neutron scattering and gradient NMR experiments have been carried out to test MCT using the molecular van der Waals liquid ortho -terphenyl as a model system. A significant anomaly of the Debye—Waller factor and a “decoupling” of self-diffusion from viscosity support the MCT predictions. A critical discussion of the relevance of such tests and of the limitations of neutron scattering is presented.
Merkel cells in ontogenesis of human nails
1993
Digital skin of human fetuses is known to contain a particularly high concentration of Merkel cells. Using antibodies against the simple epithelial cytokeratins (CK) 18 and 20, which are sensitive and specific Merkel cell markers, we studied immunohistochemically the main adnexal structure of digital skin, the nail anlage, in human fetuses (9-22 weeks of gestation) for the presence of Merkel cells. As early as week 9 some clustered Merkel cells were detected in the early matrix primordium. In specimens of week 12-15, abundant Merkel cells were found in the nail anlagen, particularly in the epithelium of the proximal nail-fold and the dorsal and ventral side of the apex region. In contrast, …
Helicity-coupling amplitudes in tensor formalism.
1993
The decay of a particle with spin to two other particles with spin is best described in the helicity formalism. It is the purpose of this paper to show that the helicity-coupling amplitudes, which appear in the angular distributions, can be expressed in terms of the covariant amplitudes in the tensor formalism. This allows for a systematic derivation for the energy dependence of the helicity-coupling amplitudes within the framework of the tensor formalism. The concept of pure intrinsic spin has been developed in the tensor formalism, for decays involving two spins in the final state, in order to bring the formalism to a form comparable to the standard $\ensuremath{\ell}S$-coupling scheme. A…
Quantitative XPS analysis of leached layers on optical glasses
1993
The corrosion of optical glasses often reduces the utility of uncoated glasses as well as the adhesion of resistive coatings deposited onto corroded glasses. Photoelectron spectroscopy (XPS) was applied to study glass surfaces with respect to their surface corrosion. In particular, leaching by the influence of polish slurries, pure water, air and even residual gases inside a vacuum device was studied in detail. Pure quartz glass and different sodium and barium silicate glasses were broken in ultrahigh vacuum (4 × 10−10 mbar) for the determination of sensitivity factors of the different XPS signals. It was found that a quantitative determination of the surface composition of corroded and lea…
Possible detection of the doubleβ+/electron-capture decay
1993
The two-neutrino double [beta] decay matrix elements of [sup 58]Ni, [sup 96]Ru, [sup 106]Cd, and [sup 136]Ce are calculated in the framework of the quasiparticle random phase approximation and the corresponding double [beta][sup +]/electron-capture (EC) decay ([beta][sup +][beta][sup +]/[beta][sup +]EC/ECEC) half-lives are estimated. The calculated ground-state-to-ground-state half-lives range from 3.9[times]10[sup 23] to 6.4[times]10[sup 19] yr indicating that the double [beta][sup +]/EC decay could, in principle, be detected using currently known experimental techniques.
A theoretical study of the electronic spectrum of thiophene
1993
Abstract The electronic spectrum of thiophene has been studied using multiconfiguration second-order perturbation theory and extended ANO basis sets. The calculations comprise four singlet valence excited states and the 3s3p3rd Rydberg series. The lowest triplet states were included and some n-π* and n-σ* states. The results have been used to assign the experimental spectrum below 8.0 eV, with a maximum deviation of about 0.1 eV for vertical transition energies. The calculations place the 2 1A1 valence state at 5.33 eV, below the 1 1B2 valence state at 5.72 eV, and the most intense valence transitions at 6.69 eV (3 1A1) and 7.32 eV (4 1B2) with oscillator strengths 0.19 and 0.39, respective…
The comparative biology of the closely related Senecio nebrodensis and S. viscosus, a narrow endemic and a widespread ruderal
1993
The closely related Senecio nebrodensis, a perennial herb from four mountain ranges in Spain, and S. viscosus, an annual herb widespread in Europe, are being compared by the study of herbarium material and comparative cultivation. In cultivation, S. nebrodensis behaved as an annual, completing its life cycle within a shorter period of time than S. viscosus. The formation of basal leaf rosettes is much more pronounced in S. nebrodensis than in S.viscosus. The main difference between the two species, however, is their breeding system. While S. nebrodensis is self-incompatible, S. viscosus is self-compatible. Differences in reproductive morphology (mainly size and number of ray florets) are su…
Adsorption et desorption de l'eau vapeur sur un polymère polyacrylique absorbant
1993
Resume Cet article porte sur la cinetique d'adsorption de l'eau vapeur sur un polymere reticule de l'acide acrylique. L'allure des courbes isocinetiques reportees dans le diagrame d'equilibre ( p , T ) est la manifestation directe de l'effet exothermique de la reaction d'adsorption et de sa consequence sur l'ecart a l'equilibre de vaporisation de l'eau; L'existence de cet effet thermique n'entraine pas de modification du mecanisme reactionnel comme ceci est indique lors d'etudes cinetiques de rehydration, ou dans les differentes approches de l'effet Smith-Topley (evaporation, deshydration, decomposition de carbonates, ou d'ammoniacales).
Low temperature optical spectroscopy of cobalt-substituted hemocyanin from Carcinus maenas
1993
In this work we report the optical absorption spectra of three cobalt-substituted derivatives of hemocyanin (He) from Carcinus maenas, in the temperature range 300–20 K. The derivatives studied are the mononuclear (Co2+)-He with a single cobalt ion in the “CuA” site, the binuclear (Co2+)2-He and the binuclear mixed metal (Co2+-Cu1+)-He. At low temperature three main bands are clearly resolved; the temperature dependence of their zeroth, first and second moments sheds light on the stereodynamic properties in the surroundings of the chromophore. Within the limits of the reported analysis, in the binuclear derivatives the motions coupled to the chromophore appear to be “essentially harmonic” i…
Covariant phase-space quantization of the induced 2D gravity
1993
Abstract We study in a parallel way the induced 2D gravity and the Jackiw-Teitelboimmodel on the cylinder from the viewpoint of the covariant description of canonical formalism. We compute explicity thhe symplectic structure of both theories showing that their (reduced) phase spaces are finite-dimensional cotangent bundles. For the Jackiw-Teitelboim model the base space (configuration space) is the space of conjugacy classes of the PSL(2, R ) group. For the induced 2D gravity, and Λ > 0, the (reduced) phase space consist of two (identical) connected components each one isomorphic to the contangent bundle of the space of hyperbolic conjugacy classes of the PSL (2, R ) group, whereas for Λ R …
Desensitization of inhibitory prejunctional alpha 2-adrenoceptors and putative imidazoline receptors on rabbit heart sympathetic nerves.
1993
To find out whether sympathetic nerves of the rabbit heart possess pharmacologically relevant prejunctional imidazoline receptors different from α-autoreceptors, the inhibition by oxymetazoline, aganodine and BDF 6143 (4-chloro-2-[2-imidazoline-2-ylamino]-isoindoline hydrochloride) of endogenous noradrenaline overflow evoked by stimulation of extrinsic postganglionic sympathetic nerves (0.66 Hz, 80 pulses) was investigated. In addition we wanted to find out whether either type of these prejunctional receptors undergoes desensitization upon pre-exposure to respective agonists. The α2-adrenoceptor agonist oxymetazoline inhibited the evoked noradrenaline overflow (2.9 nmol/l, IC50; about 90010…
Phosphodiesterase inhibitor pentoxifylline, a selective suppressor of T helper type 1- but not type 2-associated lymphokine production, prevents indu…
1993
The phosphodiesterase inhibitor pentoxifylline (POX), which is known to have pharmacological effects in animal models of multiorgan failure and endotoxin-mediated shock, was tested for its immunosuppressive potential on T lymphocyte activation in vitro and in vivo. POX was found to have a profound inhibitory effect on both mitogen- and antigen-induced proliferation of CD4+ T cells in vitro. This inhibitory activity of the drug could be reproduced by treating T lymphocytes with cAMP analogues during stimulation. Responses of repeatedly in vitro stimulated cells were much more strongly inhibited by the drug and by cAMP analogues than responses of fresh resting lymphocytes. Furthermore, POX co…
The imprints of the Great Attractor and the Virgo cluster on the microwave background
1993
A fully non-linear model based on the Tolman-Bondi solution of the Einstein equations is used to describe the Great Attractor and the Virgo cluster. The background is a Friedmann-Robertson-Walker universe, and the inhomogeneity develops from physically motivated initial profiles of the energy density and the peculiar velocity. Accurate numerical integrations of the field equations of the null geodesics are carried out, and thus the angular temperature distribution of the microwave background produced by the chosen overdensities is found. The observer is located in the Local Group. The quadrupole Q produced by each overdensity is computed and divided into two parts: the relativistic Doppler …
A combinatorial algorithm for the optimization of refraction seismics data inversion
1993
Abstract The problem of data inversion in refraction seismics can be split in two parts: data first must be preprocessed in order to determine the travel-time curve; this essentially is a geometrical problem, complicated, however, by its pattern recognition aspects. Once the geometrical problem is solved, the second part, the inversion proper, is straightforward, as the soil layering model can be calculated according to well-known algorithms. The more difficult part of the problem is the former, which implies a type of pattern recognition; because of this type of difficulty, the geometrical part of the problem usually is committed to the skill of a human operator. This paper describes an al…
Long-term results of fascial sling procedure
1993
In a retrospective study 108 patients (average age: 56.5 years) could be evaluated, who were treated with a fascial sling plasty because of pure genuine stress incontinence (n=90) or combined stress/urge incontinence (n=18). 72 patients (66.6%) had recurrent incontinence after previous surgery. The average follow-up was 5 years.
Simple and sensitive reversed-phase liquid chromatographic assay for analysis of chlorthalidone in urine
1993
Abstract This study describes a rapid method for the determination of chlorthalidone in human urine by reversed-phase liquid chromatography and UV detection at 230 nm, after clean-up over a C8 solid-phase extraction column. Liquid chromatography was carried out on a C18-bonded phase using acetonitrile-phosphate buffer (pH=3) gradient elution. Triamterene was used as internal standard. The system has been applied to the determination of chlorthalidone in the 0.10–10.0 μg/mL concentration interval; the limit of detection was 6 ng/mL.
Fractal dimension: A useful tool to describe the microgeometry of machined surfaces
1993
Abstract The authors have utilized some concepts of fractal geometry to describe the complexity of profiles surveyed from surfaces worked by cutting. In particular an experimental analysis was carried out to investigate the influence of the worked material, cutting speed and cutting operation on the “fractal dimension” parameter. The obtained results show that this parameter is able to describe the irregularities of the profile on a small scale, which is important for an overall understanding of the functional behaviour of machined surfaces. Such descriptions cannot be derived from the more commonly employed parameters.
Decreased glutathione peroxidase activity in sciatic nerve of alloxan-induced diabetic mice and its correlation with blood glucose levels.
1993
The effect of alloxan-induced diabetes on glutathione peroxidase (GSH-Px) activity in sciatic nerve of mice has been studied. We have found, 7 days after alloxan treatment, a significant decrease in this enzymatic activity in the cytosol of sciatic nerve of diabetic mice, and moreover, that these changes remained unaltered up to 21 days after alloxan injection. No modification in the glutathione content of sciatic nerve of diabetic mice was observed throughout the experiment when compared with controls. The decrease in GSH-Px activity in this tissue shows a good correlation with the increase of blood glucose levels throughout the experiment. It is hypothesized whether a combination of mecha…
Herpes virus saimiri-transformed human T lymphocytes: normal functional phenotype and preserved T cell receptor signalling
1993
Herpes virus saimiri (HVS), a primate herpes virus, transforms human CD4+ and CD8+ T lymphocytes to continuous growth in vitro. We have previously shown that HVS-transformed human T cells (HVS-T cells) respond to stimulation via CD2 with autocrine growth. In the present study we have investigated the functional characteristics of HVS-T cells. We describe that these cells can perform all the functions of normal T cells, i.e. cytokine secretion, cytotoxicity, and exocytosis of granule esterases. All these activities can be triggered via CD2 by binding to its natural ligand or via the TCR, e.g. by anti-TCR antibodies, by recognition of a bacterial superantigen and by MHC-restricted recognition…
Effects of different agents on the contractile response elicited by extracellular calcium after depletion of internal calcium stores in rat isolated …
1993
Abstract Noradrenaline, 1 μm, induced a sustained contractile response in rat isolated aorta in the presence and in the absence of extracellular Ca2+. After depleting the noradrenaline-sensitive intracellular Ca2+ stores, an increase in the basal tone of the aorta was observed during the incubation period in the presence of Ca2+ and in the absence of the agonist. We have tested the possible pathways through which Ca2+ enters the cell to refill the previously depleted Ca2+ pools, a process that is accompanied by an increase in tension. The magnitude of this increase does not depend on the presence of Mg2+ in the extracellular medium nor on the temperature, suggesting that it is mediated by a…
Inflammation-induced upregulation of NK1 receptor mRNA in dorsal horn neurones
1993
The expression of the neurokinin 1 (NK1) receptor (i.e. substance P receptor) gene in spinal cord was studied in rats subjected to unilateral inflammation by semi-quantitative in situ hybridization analysis. Low levels of NK1 receptor mRNA were detected in many neurones throughout the grey matter. Relatively strong labelling was observed in large motoneurones and a subpopulation of superficial dorsal horn neurones. Six days after Freund's adjuvant-induced unilateral hindpaw inflammation, NK1 receptor mRNA levels in lamina I/II of the dorsal horn ipsilateral to the inflamed paw increased almost two fold compared with the contralateral side. These data suggest an inflammation-induced increase…
Long-term prediction of birth weight
1993
On the basis of the hypothesis that undisturbed individual growth in fetal life keeps a constant proportional difference with the standard population 50th percentile, birth weight can be predicted with a single sonographic exploration after the 16th week of pregnancy. Data on 135 singleton pregnancies with accurate dates and delivery at term were used. Sonography was performed between the 17th and 36th weeks of pregnancy, in every case at least 4 weeks before delivery. The observed measurements of BPD, FL, and AC were used for the prediction of their values on the day of delivery, applying the Hadlock equation for the estimation of birth weight. The mean error of birth weight predictions wa…
The human complement component C8B gene: structure and phylogenetic relationship
1993
The eighth component of human complement (C8) is a serum protein that consists of three chains (alpha, beta and gamma), encoded by three separate genes, viz., C8A, C8B, and C8G. In serum, the beta-subunit is non-covalently bound to the disulfide-linked alpha-gamma subunit. Using a full-length C8 beta cDNA probe, we isolated several clones from human genomic lambda DNA libraries. Four lambda clones covering the complete cDNA sequence were characterized by TaqI restriction mapping and were "shotgun" subcloned into M13. C8 beta-cDNA-positive clones were partially sequenced to characterize the 12 exons of the gene with sizes from 69 to 347 bp. All intron-exon junctions followed the GT-AG rule. …
Flow injection flame atomic absorption analysis of Fe and Mn in cement samples
1993
A new procedure has been developed for the determination of Fe and Mn in cements. It consists in dispersing 50 mg of the solid sample in 25 ml of 0.15 mol/l HNO3 and 0.12 mol/l HCl solution. Acid slurries are heated at 50°C for 10 min and then different volumes of the slurry are injected into a water carrier stream. This previous acid treatment leaches the elements to be determined and permits the use of acid solutions as standards. For the Mn determination, the use of a single line flow injection manifold provides a limit of detection of 0.03 mgl−1 and a dynamic range up to 6 mgl−1. For the determination of Fe, the on-line dispersion of samples, using a well stirred mixing chamber, increas…
Eudesmane and elemane derivatives from Onopordon acaulon
1993
Abstract From the methanol extract of Onopordon acaulon 11 sesquiterpenes were isolated. Two elemane and three eudesmane derivatives are described for the first time.
Highly diastereoselective additions of organometallic reagents to 1-O-silylated 3,4-Di-O-benzyl-L-erythrulose derivatives
1993
Abstract The diastereoselectivity of the addition of several organometallic reagents to the carbonyl group of the title compounds has been investigated. Some organomagnesium reagents display high diastereoselectivities (90–99%) and the major products are those predicted by the α-chelation model.
Search for the standard model Higgs boson
1993
Using a data sample corresponding to about 1 233 000 hadronic Z decays collected by the ALEPH experiment at LEP, the reaction e+e- --> HZ* has been used to search for the standard model Higgs boson, in association with missing energy when Z* --> nunuBAR, or with a pair of energetic leptons when Z* --> e+e- or mu+mu-. No signal was found and, at the 95% confidence level, m(H) exceeds 58.4 GeV/c2. RI ANTONELLI, ANTONELLA/C-6238-2011; Buttar, Craig/D-3706-2011; Stahl, Achim/E-8846-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012